1. Field of the Invention
This invention relates to a two-color shifting device for a printing ribbon, utilized in a technical field of a printing device for printing various kinds of data using a printer as in, for example, a time recorder. More specifically, it relates to a two-color shifting device for a shifting device for a printing ribbon which is suitably used in various printing devices such as a time recorder.
2. Brief Description of the Prior Art
As for conventional two-color shifting devices for a printing ribbon, in which the printing color can be switched between a normal color positon such as a black color or a blue color and an abnormal color position such as a red color by switching or shifting a ribbon cassette containing a printing ribbon upwardly and downwardly relative to a printer, there are known two types. One is of the type, as disclosed, for example, in Japanese Early Laid-Open Utility Model Publication No. Sho 59-19357, in that two-color shift is made by switching or shifting the ribbon cassette upwardly and downwardly using a mechanical device. The other is of the type, as disclosed, for example, in Japanese Early Laid-Open Utility Model Publication No. Sho 56-172166, in that two-color shifting is made by moving the ribbon cassette upwardly and downwardly using a solenoid for exclusive use. At present, the two-color shifting device using a solenoid occupies a main stream because of its reliable operation.
However, the conventional two-color shifting device using a solenoid has the following problems. Since the ribbon cassette, a shifting mechanism for shifting this cassette upwardly and downwardly, and the solenoid for actuating this shifting mechanism, are required to be arranged in a vertical row, a whole device is obliged to become large, and a large mounting space is required. Moreover, since the construction of the whole device is complicated, its assembly and maintenance are troublesome, and costs thereof are high.
In view of the above, the present applicant has proposed and successfully developed a two-color shifting device for a printing ribbon, as discussed in a Japanese Utility Model application No. Hei 3-33901 which was previously filed by the present applicant, in which two-color shifting of a printing ribbon can be effected correctly using a very simple device and without using a solenoid.
The above two-color shifting device for a printing ribbon comprises a notched pinion provided with a feed gear and an intermittent gear arranged alternately in the circumferential direction, the notched pinion being slidably mounted on a guide shaft, when this notched pinion is pushed into a two-color shifting position against a compression spring by a printer which is moved in accordance with rotation of a cylindrical cam shaft, a two-piece gear mounted on a feed wheel being brought into mesh with a feed gear and an intermittent feed gear of the notched pinion, respectively, this feed wheel being rotated by a motor to cause the notched pinion to make a feed-rotation, so that a switch cam integral with the notched pinion is shifted upwardly or downwardly, thereby effecting two-color shifting of its printing color to be printed on a card.
However, the two-color shifting device for a printing ribbon thus constructed also has the following problems. In the case where the feed wheel is stopped rotation due to, for example, an electric power failure, with the two-piece gear contacting the feed gear of the notched pinion, the feed gear is readily meshed with the two-piece gear when vibration and/or impact is applied thereto. If the feed wheel starts rotation in the foregoing state because of recovery of electric power supply, the notched pinion is caused to make a feed-rotation by the two-piece gear to shift the ribbon cassette upwardly or downwardly. As a result, two-color shifting is accidentally effected at a timing when it should not be effected. The result is that an undesired color printing is made on a card by the wrong or failure ribbon shifting.